The nearest neighbor method, the bi-linear method, the bi-cubic method and the average pixel method are among the techniques that have been and are being used for dimensionally reducing images prepared by personal computers (to be referred to as PCs hereinafter).
The nearest neighbor method is a technique of adopting the density value of the pixel located closest to a pixel subjected to pixel interpolation for dimensional reduction. The nearest neighbor method is an interpolation technique that allows the quickest computation. That is, the pixels of the original image are simply thinned. Thus, the image quality tends to be degraded, e.g. apparent jaggies are generated in the dimensionally reduced image.
On the other hand, according to the bi-linear method and the bi-cubic method, the position coordinates of a pixel in the original image that correspond to the position coordinates of each pixel in a dimensionally-reduced image are determined. Then, the pixel value of each pixel in the dimensionally reduced image (density value of each pixel) is determined as equal to the average value of the pixel value of a pixel in the original image that has the corresponding position coordinates (center pixel) and of the weighted pixel values of a plurality of pixels around the subject pixel.
The average pixel method is an averaging and dimensionally reducing technique that takes into consideration the area of each pixel in the original image and the area of each pixel in the corresponding dimensionally reduced image. With the average pixel method, the least common multiple of the number of pixels of the original image and that of the reduced image are determined and the original image is expanded to the least common multiple times of the original size. Then, the expanded image is divided by the number of pixels of the reduced image and the average of the pixel values of each of the areas produced by the division is determined and used as a pixel value for the reduced image. With this arrangement, the pixel values of all the pixels in the reduced image can be determined.
With the bi-linear method, the bi-cubic method and the average pixel method, jaggies in the generated reduced image can be suppressed and hence high quality reduced images if compared with the nearest neighbor method can be provided. Particularly, the average pixel method has been and being popularly used because the pixel method can provide high quality reduced images.